Aluminum is a widely used metal for industrial products such as construction materials because of its light weight, easy processing characteristics, and high corrosion resistance owing to protection made by oxide film surrounding its surface. From processing view point, a variety of processing, such as stamping, extruding, or casting may be applied, and from alloying view point, duralumin is well known as an example. Further, it is also used in other technological fields by making use of its excellent heat conductivity or electricity conductivity. Aluminum is also a metal having potential to be used as energy source in the future, since it generates high energy when combusted, and its energy density per volume is comparable with even coal or petroleum (41.9 kJ/cm3).
From historical view point, its origin is discovery of alumina in early 19th Century, and it had been considered as precious metal until technique for isolating aluminum from alumina was established, but its availability is improved after the Hall-Heroult process was found at the end of 19th century. Detailed explanation of the Hall-Heroult process is omitted here since it is widely used today as a method for refining aluminum, but in brief, an ore called bauxite containing high percentage of alumina is melt with sodium hydroxide and extracting alumina out of it (Bayer process), the alumina is then melt in electrolytic bath (1300K) using cryolite (Ga3AlF6), and thereafter aluminum is refined by electrolysis using carbon electrodes. Carbon electrode used as anode acts as reducing agent, which combines with oxygen contained in alumina and generates carbon dioxide and carbon monoxide (1100K or more).Al2O3+3C→2Al+3COAl2O3+3/2C→2Al+3/2CO2 
Although the Hall-Heroult process is used as a major method even today for dissociating alumina, the method has problems that it consumes a large amount of electric power for dissociating alumina (electric power consumed for 1 ton of aluminum: 13,000-14,000 kWh), and further it emits a large volume of greenhouse effect gas such as CO or CO2 as shown in the above formulas. Especially, the latter problem has direct influence on warming up of the earth, hence it is a big issue on global scale to develop alternative methods for reducing alumina.
Some technological developments of the Hall-Heroult process are underway for improving its energy efficiency (for example, refer to “patent document 1”), or some alternative reducing methods that may replace the Hall-Heroult process (for example, refer to “patent document 2” and “patent document 3”) are proposed, but these counter measures would not fundamentally resolve the above mentioned problems, therefore there still remains need for drastic improvement in the method for reducing alumina.
On the other hand, magnesium is even lighter in weight compared to aluminum, and easy for processing, therefore it is a widely used metal as industrial material in the field of such as automobile, aerospace, or machinery equipment, and it is also used as an additive for improving mechanical characteristics of a variety of materials. From processing view point, extruding, stamping, forging etc. may be applied, therefore it may cover a wide range of industrial application. Although it tends to be corroded due to its relatively high chemical activity, it is possible to make it in stable condition by applying surface treatment. It is also known that it generates a large amount of energy when it is combusted (601.7 kJ/mol).
Historically, commercial production of magnesium was started in late 19th century, almost the same timing as aluminum, but timing of wide use of it became somewhat belated due to difficulty of its refining process. Thermal reduction method and electrolytic method are known today as methods for refining magnesium. In the former method, which is a major method today, magnesia obtained by burning dolomite ore is reduced by adding reducing agent and heating it at high temperature under low pressure (known as the Pidgeon process).2MgO+Si→SiO2+2Mg
In the latter process, magnesium is obtained by electrolyzing mercuric magnesium gained mainly from sea water (known as electrolysis refining process).MgCl2→Mg+Cl2 
However, since both of these processes are the same in a sense that a large amount of electric power needs to be consumed, a novel method for refining magnesium with low energy consumption is also required.